Since the invention and introduction of Portland cement-based, self-leveling underlayments in the U.S. in 1978, sub-floor preparation technologies, means and methods have continuously evolved. This evolution has been driven by dynamic market forces, including more manufacturers, a larger and more experienced installer base, increased adoption rates with a wider range of applications, ever-increasing project sizes and complexity, new flooring structures with more demanding requirements, the ability to handle high moisture levels with less surface preparation and fast track construction.